Plant Nutrition :: Plant Growth Regulators


  • Auxin is a greek word  which means to increase.
  • It is a generic term for chemicals that typically stimulate cell elongation, but auxins also influence a wide range of growth and development response.
  • The chemical isolations and characterization was done by Kogi et al. (1934).
  • Auxins are the first identified hormones of which IAA seems to be the major naturally  occurring, endogenous auxin  in  crops.
  • Besides IAA, plants contain three other compounds which are structurally similar and elicit many of the same response as that of IAA, 4, chloroindole acetic acid (CIAA),phenylacetic acid (PAA), indole butyric acid (IBA).
  • Synthetic compounds are classified into five major categories; indole acids, naphthalene acids, chlorophenoxy acids, benzoic acid and picolinic acid derivatives.

Role of Auxin

1 Cell divisions and enlargement Eg. cambial growth in diameter .IAA + GA
2 Tissue culture Shoot multiplications (IBA and BAP),callus Growth (2,4,-D), root multiplication IAA and IBA (1-2 mg)
3 Breaking dormancy and Apical dominance NAA
4 Shortening internode Apple trees (NAA) (dwarf branch-fruit)
5 Rooting of cuttings (10-1000 ppm - NAA, IAA, phenyl acetic acid)
6 Prevent lodging NAA- develop woody and erect stem
7 Prevent abscission Premature leaf, fruit, flower fall
(NAA, IAA and 2,4-D)
8 Parthenocarpic fruit Grapes, banana, orange - (IAA)
9 Flower initiations Pine apple -uniform flowering - fruit ripening (NAA). Delay flowering (2,4-D)
10 Weed eradications 2,4,D and  auxin compounds


Preventing fruit abscission
Tissue culture: Callus growth and Shoot multiplication



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